The proposed project is designed to 1) characterize and determine the total number of cooperatively interacting substrate binding sites of platelet myosin using equilibrium and spectroscopic techniques; 2) rapid mixing techniques such as stopped flow apparatus will be used to delineate positive and negative cooperative interactions of substrate binding in platelet myosin; 3) studies described under (1) and (2) will also be performed with enzymatically active subfragments (heavy meromyosin and S-1) of platelet muscle myosin; 4) the binding of the substrate (C14ATP, C14ADP) to phosphorylated platelet myosin will be studied and the kinetic parameters will be compared with unphosphorylated myosin; 5) transient kinetic techniques (stopped flow apparatus) will be used to investigate the biochemical mechanism of ATPase of platelet myosin both in the phosphorylated and unphosphorylated form, particularly to learn and characterize the intermediates involved in the overall mechanism. Comparison of this interaction will be made with already established skeletal muscle myosin ATPase; and 6) effect of platelet actin upon the binding of ADP to platelet myosin and its subfragments will be carried out.